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Renovation of the attic floor slab
Thermal insulation between the attic floor joists: the work is carried out from above, from the attic, without touching the ceiling of the room below.
Technical content: Bogdan Ivănescu, graduate engineer, PhD candidate at the Technical University of Cluj-Napoca · updated on 16.10.2026
Three zones, each with its own role
The boarding is lifted, the old insulation is removed and the bays between the joists are cleaned. In each bay, Reflectiva Gold is laid along the entire perimeter, followed by Wolle thermal insulation fibre over the full height of the joist. Finally, the boarding is put back in place and once again becomes the attic floor.
The ceiling is not lowered at all
All the insulation fits between the joists, so the room height remains the same: 0 cm lost.
Gold sits on the warm side
Reflectiva Gold stops the vapour rising from the house, which is why it is placed beneath the Wolle, on the bottom and sides of the bay. It is cut at the upper edge of the joist, and the top face of the joist is left uncovered so that moisture in the timber can evaporate.
Slabs supplied at the width of the bay
Wolle slabs are supplied at the width of the clear spacing between the joists plus 1 cm; for example, for a clear spacing of 55 cm you receive slabs of 56 cm. They are fitted under compression, without gaps, and do not need to be cut in the attic.
As high as the joist
The thickness of the insulation is equal to the height of the joist. With 15 cm joists, the 5 cm layer is installed first, at the bottom, followed by the 10 cm layer on top. The 5 cm layer adheres very well to the porosity of the substrate and requires no anchoring whatsoever.
Distance from the chimney
Around the chimney and any strong heat source above 120 °C, leave a clear zone of 50 cm all around.
Emissivity 0.05
Reflectiva Gold has an emissivity of 0.05 and a reflectivity of 95–97%.
Emissivity: an emissivity of 0.05 means that the aluminium face radiates only 5% of the heat that an ordinary surface would radiate, and therefore does not give off heat by radiation. The lower it is, the better. What this means →Reflectivity: the proportion of the radiant heat reaching the membrane that is sent back. What this means →Installation steps
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Products for this application
Warranty
- ✓Reflectiva Gold: 50-year warranty, service life of at least 50 years
- ✓Wolle thermal insulation fibre: 50-year warranty (including against settlement and disintegration)
Frequently asked questions
Do I need to dismantle the room ceiling?
No. The work is carried out from above, from the attic: lift the boarding, insulate between the joists and refit it. The ceiling remains untouched.
Why does Gold not also cover the top face of the joist?
Gold is cut at the top edge of the joist so that the top face remains exposed and moisture in the timber can evaporate.
Do I need to cut Wolle in the attic?
No. The boards are supplied at the width of the clear space between the joists plus 1 cm and fit under compression, without gaps.
Do the Gold strips overlap?
No. They are butt-jointed, and the joints and corners are sealed with Power Tape.
What should I do around the chimney?
Around the chimney and any strong heat source above 120 °C, leave a clear zone of 50 cm all around.